Treadmills have become popular in recent years for both home and office use to enable exercisers to run indoors in small confines. Most exercise treadmills include first and second roller assemblies rotatably mounted across opposite ends of a frame. Each roller assembly includes a cylindrical roller that is journaled on an axle or opposing stub shafts, with the axle or stub shafts being secured to opposite sides of the treadmill frame. A belt is then trained about the roller assemblies. The distance between the first and second roller assemblies determines the tension in the treadmill belt. The tension in the treadmill belt is initially set to provide a firm footing for the exerciser without slack that could result in injury to the exerciser, and to prevent undesirable side-to-side movement of the belt on the roller assemblies.
Over time with repeated usage, the bearings on which the rollers are journaled tend to wear, and the belt material may stretch. In order to initially set the treadmill belt tension and to later enable adjustment for this wear, many treadmills include an adjustment mechanism whereby the position of one of the roller assemblies can be adjusted relative to the frame and the other roller assembly by the exerciser. In some conventional models, this mechanism may include a bolt that is longitudinally disposed and rotatably mounted on the frame, and that has a threaded end that is engaged within a threaded cross-hole formed through one end of the roller assembly axle. Rotation of the bolt results in movement of that end of the axle along the length of the bolt, changing the distance between the roller assembly axles. The other end of the axle may also be adjustably mounted to the frame with a similar adjustment bolt to enable the roller assemblies to be maintained in parallel relationship.
A drawback of such conventional treadmill belt tensioning adjustment mechanisms is that the exerciser may inadvertently or purposefully overtighten the belt by drawing the axles too far apart from each other. This can result in excessive wear of the belt and the roller bearings, shortening the life of the treadmill.